1. Field of the Invention
The present invention relates to a control apparatus for a vehicle for controlling braking force while the vehicle is stopped.
2. Description of Related Art
An idle-stop technology in which the engine is stopped during stop of the vehicle when a predetermined condition is satisfied, is known. Also, there has been known an engine-restart technology in which the engine which has been stopped by the idle-stop technology is restarted when the driver's foot is moved away from the brake pedal. The both technologies are collectively called idle-stop function, start & stop function, engine • automatically • start • stop function, or the like (hereinafter, simply referred to as idle-stop function).
In addition, there has been known a technology in which a traveling following a preceding vehicle with an inter-vehicle distance corresponding to vehicle speed is performed while the preceding vehicle is captured, and a traveling at a preset constant speed is performed if no preceding vehicle is captured, and which is referred to as constant-speed traveling • inter-vehicle distance control function and/or ACC (Adaptive Cruise Control) or the like (hereinafter, referred to as inter-vehicle distance control function). Moreover, a full vehicle speed range inter-vehicle distance control function in which the host vehicle is also stopped if the preceding vehicle is slowed down to stop and the host vehicle is also started if the preceding vehicle is started, is known as a mode of the inter-vehicle distance control function.
By equipping the vehicle with the idle-stop function and the full vehicle speed inter-vehicle distance control function, it is possible to enable the idle-stop function to stop the engine after the host vehicle is stopped by the full vehicle speed inter-vehicle distance control function (for example, refer to Japanese Patent Application Publication No. 2012-206593 (JP 2012-206593 A)). In JP 2012-206593 A, a cruise control system is disclosed, in which when the host vehicle is stopped by the full vehicle speed inter-vehicle distance control function, a holding force for keeping the vehicle in the stop state is generated, and when a condition to automatically stop the engine is satisfied, the engine of the host vehicle is automatically stopped.
However, in JP 2012-206593 A, since only the holding force for keeping the stop state is generated, there is a problem that the vehicle is likely to move when the engine is restarted by the idle-stop function.
FIG. 1A is a structural view showing that the rotation of the engine is transmitted up to the tire. For the vehicle which has been stopped by the full vehicle speed inter-vehicle distance control function, since the shift lever is set at D position, the rotation of the engine is transmitted to the tire via a torque converter and a transmission.
FIG. 1B is an exemplary diagram explaining the relationship between the driving force and the braking force. The vehicle which has been stopped by the full vehicle speed inter-vehicle distance control function is stopped with a minimum braking force required for maintaining the stop state of the vehicle. Since the opening degree of the throttle is zero, the engine is in an idle state, and thus the braking force is a braking force required at the idle-stop of the vehicle.
On the other hand, for the engine which is just restarted by the idle-stop function, since its rotation speed is higher than that in the idle state (due to the speed increase of the engine), a driving force larger than the braking force for stopping the vehicle is generated. As a result, there is a possibility that the driving force surmounts the braking force to move the vehicle.
Although it may be considered that the braking force is increased in advance by anticipating this inconvenience, since the lower the pressure of the braking fluid for generating the braking force is, the shorter the time taken to reduce the pressure is, the responsiveness at the vehicle start by the full vehicle speed inter-vehicle distance control function will be increased. Thus, it is not preferable to increase the braking force. In addition, increasing the braking force is not preferable due to its useless energy consumption.